Medical endoprosthesis or implants for a wide variety of applications are known from the state of the art in great diversity. Implants as defined by the present invention shall be endovascular prostheses or other endoprostheses, such as stents (vascular stent, bile duct stent, mitral stent), endoprostheses for closing patent foramen ovale (PFO), pulmonary valve stent, endoprosthesis for closing an atrial septal defect (ASD), prosthesis in the area of hard and soft tissue, and also anchoring elements for electrodes, in particular pacemakers or defibrillators.
These days, stents that are used for the treatment of stenoses (vascular constrictions) are employed especially frequently as implants. They have a body in the shape of an optionally perforated tubular or hollow-cylindrical basic structure, which is open at both longitudinal ends. The basic structure of the stent can be composed of individual mesh sections, which are formed by zigzag- or meander-shaped struts. The tubular basic structure of such an endoprosthesis is inserted into the vessel requiring treatment and is intended to support the vessel. Stents have become established especially for the treatment of vascular diseases. Constricted areas in the vessels can be expanded through the use of stents, resulting in increased lumen. While through the use of stents or other implants, an optimal vessel cross-section can be achieved, which is primarily necessary for a successful therapy, however the lasting presence of such a foreign object triggers a cascade of microbiological processes, which favor inflammation of the vessel to be treated or necrotic vascular changes, for example, and due to the formation of plaque may result in gradual blockage of the stent.
Stent grafts refer to stents which on or in their frequently lattice-shaped basic structure also contain a nonwoven fabric, or another planar covering, such as a film. Here, a nonwoven fabric shall be understood as a textile surface structure which is formed by individual fibers. The term nonwoven fabric in the present invention also includes the case where the textile surface structure is made of only a single “endless” fiber. Such a stent graft is used, for example, to reinforce weak spots in arteries, such as in the region of an aneurysm, or a rupture in the vessel wall (bail-out device), in particular as an emergency stent.
Known stents, which as stent grafts are provided with a PTFE film or an ePTFE film, exhibit poor ingrowth behavior in the vascular system due to the film structure. In a variant of a stent graft known from the prior art, for example, an ePTFE film is disposed in a sandwich-like manner between two stent lattice structures. It has been shown that such a stent graft is very rigid, so that it has an increase restenosis rate due to the increased flexural strength of the sandwich structure. The ePTFE film structure has worse endothelialization and poorer transmural communication. Furthermore, such a “sandwich” stent graft is difficult or impossible to apply to the desired lesion, particularly in the case of tortuous vessel anatomy.
The published prior art WO 03/087443 A1 describes a fiber-like covering for a stent, which is applied onto the supporting structure by way of electrospinning. In this published prior art, the fiber materials used are PET, PLA, PGA, or PCL. Although the stent grafts produced from these materials have comparatively high porosity, so that in critical regions the flow in the capillaries of the wall of the vessel being treated is ensured, and therefore good endothelialization can be achieved, an increase rate of complications was observed with such an electrospun stent graft.
From the document CA 2 567 954 A1, a stent graft is known, in which better bonding of the graft material to the respective strut is to be achieved by suturing the graft material in the region of the struts and/or by using a washer on a strut. Yet, the rate of complications was not reduced by fixing the graft material in this manner.